Table 2.

Microcirculatory variables.

Microcirculation variable	Information provided	Measurement
Microvascular flow index (MFI)	Perfusion quality	Image divided in to quadrants. A number is assigned to each quadrant according to predominant flow type (0 = no flow, 1 = intermittent, 2 = sluggish, 3 = continuous). The MFI results from the mean of the four values.
Total vessel density (TVD)	Vessel density	The total length of the vessels divided by the total surface area of the analysed area.
Perfused vessel density (PVD)	Functional vessel density	Total length of perfused vessels (MFI score 2/3) divided by the analysed area.
Proportional of perfused  vessels (PPV)	Perfusion quality	100 * number of perfused vessels divided by the total number of vessels.
Heterogeneity index (HI)	Measure of the heterogeneity of flow between vessels.	Highest MFI – lowest MFI divided by mean MFI across all sites analysed.